This invention is related to the use of catheter systems for treating certain conditions within the body of a patient and in particular the use of protective sheaths for covering parts of the catheter system while the system is being positioned within the patient""s body.
A catheter system is used to deliver various therapeutic treatments to remote sites within a patient""s body. A therapeutic device located near the distal end of the catheter system is positioned by advancing the catheter system through the tortuous curves of the patient""s vasculature until the therapeutic device is in the proper position. An example of one such therapeutic device is an intravascular stent for holding open and maintaining the free passage of fluids in an artery or other vessel. A stent often may be deployed following a percutaneous transluminal coronary angioplasty (PTCA). In a PTCA procedure, a guiding catheter having a preformed distal tip is precutaneously introduced into the cardiovascular system of the patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated at the ostium of a desired coronary artery. A guide wire is positioned within an inner lumen of a dilatation catheter having an inflatable balloon on the distal and both the catheter and guide wire are advanced through the previously placed guiding catheter to its distal end. The guide wire is first advanced out of the distal end of the guiding catheter and into the vasculature of the patient until the distal end of the guide wire crosses the lesion to be dilated. The dilatation catheter, with its distally mounted balloon, is then advanced out of the distal end of the guiding catheter over the guide wire until the balloon is properly positioned to dilate the narrowed region. The balloon is then inflated with a radiopaque fluid to a predetermined size to dilate the artery in the stenotic region. The balloon is then deflated and the catheter removed leaving the newly dilated artery with increased blood flow. In some cases the inflation of the balloon during angioplasty causes a dissection of the arterial lining or generally weakens the arterial wall in the area where the balloon was inflated. When the balloon is deflated after such a dilation, blood can flow between the arterial wall and the dissected lining, constricting the flow passage or causing a section of the lining to be forced into the flow thereby partially or completely blocking the blood flow in the artery. A stent is often used to re-secure a dissected lining in the artery wall.
Stents are well known tubular devices which, when expanded, contact the walls of a body lumen and maintains an open passage through the lumen. A stent delivery system often consists of an elongated catheter with an inflatable balloon on the distal end with an expandable stent mounted tightly around the inflatable balloon. The catheter is advanced over the in-place guide wire and then through the guiding catheter, out the distal tip of the guiding catheter and then through the patient arterial system until the stent is located at the site of the dissected arterial lining. The balloon is inflated causing the stent to expand and force the arterial lining back into place. The stent is expanded into contact with the walls of the artery at the site of the dissection and remains in an expanded state and opposed to the artery wall, holding open the artery after the balloon is deflated and the catheter and balloon are withdrawn from the patient. In an alternative procedure, an angioplasty may be performed with a stent over the dilation balloon thereby dilating the artery and ensuring its patency with a stent in one procedure.
Several problems can occur during the insertion of the stent delivery system, or any other device attached to the distal end of a delivery catheter, into the patient. One problem is that the device may become damaged on the way to the treatment site. For example, a stent may become dislodged from the balloon. This occurs when the stent bumps into the walls of the artery as it travels through the tortuous anatomy of the patient""s vasculature. A second related problem is damage to the walls of the body lumen due to abrasion by the device as it passes through the vasculature. For example, a stent which often has an open lattice-like structure may present a relatively rough surface, abrading the walls of the body lumen as it passes. A third problem encountered during the insertion of the catheter system is the difficulty in advancing the leading edge of the relatively blunt end of the device such as a balloon and stent assembly past stenosed regions of the patient""s arteries and ultimately past the obstruction to be repaired. This can be especially difficult in arteries with calcified deposits.
Finally, there are situations when a delivery catheter needs to be removed without first delivering the device such as when a stent cannot be delivered because of an unpassable obstruction or other complication. In this situation, the delivery catheter must be withdrawn and the stent must pass back through the distal port of the guiding catheter. There is a potential danger that the stent will become dislodged as it traverses the distal port of the guiding catheter. It may be the case that the guiding catheter must also be withdrawn if an undeployed device such as an unexpanded stent is to be removed safely.
One solution to the problem of abrasion between the device to be delivered and the walls of the body lumen is to enclose the device or the entire distal end of the device delivery system in a protective cover or sheath.
The prior art discloses catheter systems with pre-attached sheaths, which are typically incorporated onto the catheter system when the catheter is manufactured. Several examples of these types of sheath systems can be found in U.S. Pat. No. 4,733,665 to Palmaz, U.S. Pat. No. 5,458,615 to Klemm et al., and U.S. Pat. No. 5,158,548 to Lau et al.
Additional reasons for using a sheath with the delivery catheter system can include the overall poor condition of the patient""s vasculature and where there is an increased risk of damage or embolism. Additionally, unexpected obstructions encountered during the dilation phase of the PTCA may, in the opinion of the physician, warrant the use of a sheath.
While there are several reasons that warrant use of a sheath to cover a device such as a stent, there also are factors which mitigate against using a sheath. One such factor is the additional time required to retract or remove the sheath from the device to be deployed. This is important when the physician wishes to minimize the time an artery is blocked by the device and where the size of the device is large relative to the size of the vessel. Another factor is that the addition of a sheath may make the overall outer diameter of the catheter too large to safely reach the treatment site. Another situation where the added complexity of using a sheath may not be warranted is when the blockage in the patient""s artery is very close to the distal end of the guiding catheter so that the distance the delivery catheter must travel through the arteries is small. Here the opportunity for damage to either the device to be delivered or the walls of the patient""s vasculature may be minimal.
As indicated above, some catheter systems include sheaths when they are manufactured so that the physician has no choice but to use the sheath, even if the application does not require the added protection provided by the sheath or warrant the added complexity.
What has been needed and heretofore unavailable is a sheath with a low profile to aid in catheter insertion which may be selected and added to a catheter system by the physician based on the condition encountered, thereby allowing the flexibility of using a sheath with a variety of catheter systems not originally designed to use a sheath.
This invention is directed to a protective sheath for covering a catheter delivery system which travels over a guide wire. The catheter delivery system is adapted to deliver a therapeutic device such as an intravascular stent to a position within a patient""s vasculature. The design of the sheath is flexible enough to be used with a range of catheter systems not originally fitted with protective sheaths and allows the physician to retrofit a catheter to adapt to unexpected conditions.
The sheath of the present invention allows for the rapid and safe deployment of the therapeutic device within the patient""s vascular system or other bodily lumen while protecting the therapeutic device from becoming prematurely dislodged or damaged and protecting the body lumen from abrasion from the therapeutic device as it passes through the body lumen. The sheath also provides a more streamlined profile for the catheter system as it passes through the body lumen thereby reducing the effort required in inserting the device and reducing the trauma to the walls of the body lumen. The design is such that the sheath could be added to catheter systems originally designed without a sheath when the use of a sheath is warranted in the opinion of the physician. Finally, the sheath allows the withdrawal of an undelivered device back into a previously inserted guiding catheter thereby avoiding the premature removal of the guiding catheter.
The sheath is composed of an adapter, a body, a protective section, and a tip section. The adapter serves two functions. One function is to prevent back-flow of blood; the second function is to provide a port to allow flushing of the device with saline or another fluid before insertion into the patient. The body provides a means for providing translational motion of the sheath relative to the enclosed, protected, catheter. In one preferred embodiment the body is a tube. The protective section rests over the distal end area of the enclosed catheter and isolates the area from any of the forces generated during advancement to the treatment site. One unique feature of this device is the manner in which the protective section smoothly transitions to the tip section. In a preferred embodiment, a notch is formed in its entirety within a tapered outer wall surface of the reduced cross section distal end of the protective section adjacent to the distal tip between the protective section and the tip to allow the sheath to be retracted relative to the protected area, thereby exposing a therapeutic device such as a stent. This notch is formed within the surface of the tapered outer wall and is distinct and proximally placed from the distal tip. In other embodiments, the tip is shaped to closely match the profile of the therapeutic device, and may thus encompass folds, slits, or be otherwise specially shaped.
The sheath will have an inner diameter large enough to accommodate the intravascular catheter and to allow the catheter free longitudinal movement therein. In an alternate embodiment the protective section could have an inner diameter such that the protective section must be stretched slightly to enclose the device disposed on the distal end of the delivery catheter thereby providing a secure fit.
An important feature of the invention is that the sheath can be added to a catheter system based on the judgment of the physician at the time of the procedure. This allows the physician to adapt to conditions encountered during the procedure.
Another feature of the invention is that this sheath design can be used with any catheter system which uses a guide wire. Although, optimal performance should result when a sheath is matched at least in inside diameter and overall length to a particular catheter system.
An important feature of the invention is the tapered end section of the protective section. This tapered end facilitates the advancement of the catheter system by reducing the frontal area presented by the catheter as it travels through the patient""s vasculature. Additionally, the sheath may be coated, such as with a silicone or a hydrophilic coating, to further reduce the effort required to advance the device through the vasculature and/or increase the ability of the device to cross a lesion or a region of stenosis. The sheath of the present invention thus allows the use of coatings that may not otherwise be desirable for use with a typical stent delivery catheter due to possible contamination of the stent by the coating substance.
The sheath may be made of a variety of materials. Most simply, a polymeric material may be used. The tubular body of the sheath need not be made of the same material as the protective section or the tip section. For example, the protective section could be made of a woven material such as fabric. Additionally, a felt or non-woven material could also be used. The material chosen for the protective section must have sufficient flexibility to allow usage of the underlying catheter in its usual manner.
The tip of the sheath can be either the same material as the protective section, or can be of entirely different construction altogether. This flexibility in design is an important feature of this invention. This flexibility allows the tip to be designed for optimal access to a lesion and crossing thereof.
The primary function of the body of the sheath is to allow for movement of the protective section relative to the enclosed catheter. The body could be as simple as an elongated member attached to the protective section and extending out of the patient""s body to allow the protective section to be retracted. In the preferred embodiment, the body is a tube through which the catheter is inserted. The tube may be made from a variety of polymers or even metal. Additionally, the tube may have one or more holes (exit ports) near its distal end to allow a guide wire to pass through should the enclosed catheter be of the well-known rapid-exchange (RX) type.
In a preferred method of using the sheath with a balloon catheter containing a stent, the catheter assembly with the stent mounted thereon is inserted through the sheath adapter and advanced through the sheath until the tip of the catheter/stent abuts the tip of the sheath. A guide wire is inserted through the distal tip of the sheath and through the distal tip of the catheter. The sheath-catheter/stent assembly is advanced over the guide wire similar to a dilatation catheter. The sheath may be formed with one or more exit ports near the distal end, or alternatively with full or partial slits extending to the proximal portion, so that if a catheter/stent of the rapid-exchange (RX) type is used, the guide wire can exit through the sheath.
Once the sheath system is advanced to the treatment site, the guide wire is retracted proximally into the dilation catheter. The purpose of withdrawing the guide-wire is to disengage it from the tip of the sheath. The sheath is now capable of being retracted proximally to expose the underlying stent. Once the guide wire is disengaged from the sheath tip, it is possible to re-advance the guide wire through the notch in the protective section and distally into the artery and distal of the treatment site. The relative axial position of the delivery sheath and the intravascular catheter having the stent thereon is adjusted to urge the distal end of the vascular catheter out of the notch in the protective section to expose the expandable stent. Either the catheter can be advanced distally with respect to the sheath or the sheath may be withdrawn proximally with respect to the catheter or both movements could be employed. Once the stent is completely out of the delivery sheath, the expandable member on the intravascular catheter can be expanded to expand the stent into contact with the vessel in a known manner.
While the present invention has been described herein in terms of delivering expandable stents to locations within a patient""s body lumen, the sheath of this invention can be used to protect most catheters which utilize a guide wire and which are used to perform procedures involving other devices in other locations within any body lumen. Various changes and improvements may also be made to the invention without departing from the scope thereof.